OTHER METEORIC STREAMS.
_The Meteors of August 7-11._--Muschenbroek, in his "Introduction to
Natural Philosophy," published in 1762, stated as the result of his own
observations that shooting-stars are more abundant in August than in any
other part of the year. The fact, however, that a maximum occurs on the
9th or 10th of the month was first shown by Quetelet in 1835. Since that
time the shower has been regularly observed both in Europe and America;
the number of meteors at the maximum sometimes amounting to 160 per
hour. Their tracks when produced backward intersect each other at a
particular point in the constellation Perseus.
Of the 315 meteoric displays given in Quetelet's catalogue, 63 belong to
the August epoch. Their dates up to the commencement of the present
century are as follows:
1. A.D. 811, July 25th.
2. 820, " 25th-30th.
3. 824, " 26th-28th.
4. 830, " 26th.
5. 833, " 27th.
6. 835, " 26th.
7. 841, " 25th-30th.
8. 924, " 27th-30th.
9. 925, " 27th-30th.
10. 926, " 27th-30th.
11. 933, " 25th-30th.
12. 1243, Aug. 2d.
13. 1451, " 7th.
14. 1709, " 8th.
15. 1779, " 9th-10th.
16. 1781, " 8th.
17. 1784, " 6th-9th.
18. 1789, " 10th.
19. 1798, " 9th.
20. 1799, " 9th-10th.
21. 1800, " 10th.
As the earth is about five days in crossing the ring, its breadth in
some parts cannot be less than 8,000,000 miles.
In 1866 Professor Schiaparelli, on computing the orbit of this meteoric
stream, noticed the remarkable agreement of its elements with those of
Swift's or Tuttle's comet[25] (1862, III.), as computed by Dr. Oppolzer.
These coincidences are exhibited in the following table:
Meteors of Comet III.
August 10. of 1862.
Longitude of perihelion 343° 38´ 344° 41´
Ascending node 138° 16´ 137° 27´
Inclination 63° 3´ 66° 25´
Perihelion distance 0.9643 0.9626.
Period 105 years (?) 121.5 years.
Motion Retrograde. Retrograde.
[25] Mr. Swift, of Marathon, N. Y., had two or three days priority
in the discovery of this comet, but unfortunately delayed his
announcement of the fact.
It appears, therefore, that the third comet of 1862 is a part of the
meteoric stream whose orbit is crossed by the earth on the 10th of
August.
The characteristics of different meteor-zones afford interesting
indications in regard to their relative age, the magnitude and
composition of their corpuscles, etc. Thus, if we compare the streams of
August 10 and November 14, we shall find that the former probably
entered our system at a comparatively remote epoch. We have seen that at
each return to perihelion the meteoric cluster is extended over a
greater arc of its orbit. Now, Tuttle's comet and the August meteors
undoubtedly constituted a single group previous to their entering the
solar domain. It is evident, however, from the annual return of the
shower during the last 90 years, that the ring is at present nearly if
not quite continuous. That the meteoric mass had completed many
revolutions before the ninth century of our era is manifest from the
frequent showers observed between the years 811 and 841. At the same
time, the long interval of 83 years between the last observed display in
the ninth century, and the first in the tenth, seems to indicate the
existence of a wide chasm in the ring no more than a thousand years
since.
Neither the period of the meteors nor that of the comet can yet be
regarded as accurately ascertained. The latter, however, in all
probability, exceeds the former by several years. Now, at each passage
of the earth through the elliptic stream, those meteoroids nearest the
disturbing body must be thrown into orbits differing more or less from
that of the primitive group. In like manner the near approach of the
_comet_ to the earth at an ancient epoch may account for the lengthening
of its periodic time.
The Meteors of November 27.
Professor Schiaparelli's brilliant discovery of the relation between
comets and meteors may now be ranked with the established truths of
astronomy. His hypothesis, however, in regard to the _origin_ of
meteoric streams has not been generally accepted. Comets and meteors,
according to his theory, are derived from cosmical clouds existing in
great numbers in stellar space. These nebulæ, in consequence of their
own motion or that of the sun, are drawn towards the centre of our
system. By the unequal influence of the sun's attraction on different
parts, such clouds are transformed into currents of great length before
reaching the limits of the planetary system. Shooting-stars, fire-balls,
aerolites, and comets being all of the same nature, differing merely in
size, sometimes fall towards the sun as parts of the same current.
The views of Dr. Weiss, of Vienna, differ from those of Schiaparelli, in
that he regards comets as the original bodies by whose disintegration
meteor-streams are gradually formed.[26] "Cosmical clouds," he remarks,
"undoubtedly appear in the universe, but only of such density that in
most cases they possess sufficient coherence to withstand the
destructive operation of the sun's attraction, not only up to the
boundaries of our solar system, but even within it. Such cosmical clouds
will always appear to us as comets when they pass near enough to the
earth to become visible. Approaching the sun, the comet undergoes great
physical changes, which finally affect the stability of its structure:
it can no longer hold together: parts of it take independent orbits
around the sun, having great resemblance to the orbit of the parent
comet. With periodical comets, this process is repeated at each
successive approach to the sun. Gradually the products of disintegration
are distributed along the comet's orbit, and if the earth's orbit cuts
this, the phenomenon of shooting-stars is produced."
[26] _Astr. Nach._, Nos. 1710, 1711. For a fuller statement of
Schiaparelli's theory, see Silliman's Journal for May, 1867.
These views of the distinguished astronomer of Vienna are confirmed by
the star-shower of November 27, 1872. That the orbits of the earth and
Biela's comet intersect at the point passed by the former about the last
of November, and that in 1845 the comet separated into two visible
parts, has been stated in a previous chapter. The comet's non-appearance
in December, 1865, and in September, 1872, was regarded by astronomers
as presumptive evidence of its progressive dissolution. A meteoric
shower, resulting from the earth's collision with the cometary _débris_,
was accordingly expected about the 27th of November.
The first indication of the approaching display appeared on the evening
of November 24, when meteors in unusual numbers were observed by
Professor Newton, at New Haven, Connecticut. On Wednesday evening, the
27th, from the close of twilight till 8 o'clock, a decided shower of
shooting-stars was noticed in various parts of the United States. At
Greencastle, Indiana, Professor Joseph Tingley counted 110 meteors in 40
minutes, and at Princeton, in the same State, Mr. D. Eckley Hunter
counted 70 in 80 minutes. The numbers seen at New Haven were
considerably greater. The fact that the display commenced before
daylight had entirely closed seemed to indicate that only the
termination of the shower had been observed in this country. Accordingly
the display was soon found to have been witnessed from 60° E. to 90° W.
of Greenwich, or through 150° of longitude. In England the first bolide
of the swarm was seen by M. M. Brinkley, at 3 o'clock, P.M., in full
daylight. The meteors were most numerous in the southern part of the
continent, particularly in Italy. At the Observatory of Breslau,
according to M. Faye, 3000 were seen from 6h. 30m. to 7h. 50m. Dr. Heis
reported that at Münster 2500 per hour were counted by two observers. At
Naples, Signor Gasparis observed two meteors per second. At Turin, M.
Denza, Director of the Observatory, reported 33,400 in 6h. 30m.; many of
various and delicate colors, and followed by long and brilliant trains.
At some points the numbers were so great that an accurate enumeration
was wholly impossible. In short, the display was decidedly the most
brilliant that has occurred since that of November 13, 1833.
But some of the most interesting circumstances in connection with the
phenomena of November 27, 1872, remain to be detailed. Astronomers
without exception regarded the display as due to the earth's passage
through the _débris_ following in the path of Biela's comet. In
accordance with this view Dr. Klinkerfues, of Gottingen, concluded that
the comet itself, or rather its largest portion, ought to be found in
the region of the heavens nearly opposite to that from which the
meteoroids appeared to radiate.[27] As this point in the southern
hemisphere could not be observed in Europe, he conceived the happy idea
of detecting the fugitive _by means of the electric telegraph_. The
following was accordingly dispatched to Mr. Pogson, Director of the
Government Observatory at Madras, in Southern India: "_Biela touched
earth on 27th; search near Theta Centauri_." The first two mornings
after the receipt of this dispatch were cloudy at Madras. On the third,
however, the cometary fragment was found, and its motion accurately
measured. The observer described it as circular and rather bright, with
no traces of a tail. But one fragment could be detected. On the next
morning, December 3, the comet was again observed. Its diameter had
sensibly increased; it had a bright nucleus, and still presented a
circular aspect. A faint tail was also noticed, equal in length to
one-fourth of the moon's apparent diameter. The following mornings being
again cloudy, no further observations could be obtained. This cometary
mass will be in close proximity to the earth about the last of November,
1892. Another brilliant meteoric shower may therefore be expected at
that epoch.
[27] The radiant of the Biela meteors is near _Gamma Andromedæ_.
The Meteors of April 20.
Meteoric showers have occurred about the 20th of April in the following
years:
B.C. 687
15
A.D. 582
1093 }
1094 }
1095 }
1096 }
1122 }
1123 }
1803
The probability that these meteors are derived from a ring which
intersects the earth's orbit, was first suggested by Arago in 1836. A
comparison of dates led Herrick to designate 27 years as the probable
period of the cluster. In the _Astronomische Nachrichten_, No. 1632, Dr.
Weiss called attention to the fact that the orbit of the first comet of
1861 very nearly intersects that of the earth, in longitude 210°--the
point passed by the latter at the epoch of the April meteoric shower. A
relation between the meteors and the comet, indicating an approximate
equality of periods, was thus suggested as probable. But the comet,
according to Oppolzer, does not complete a revolution in less than 415
years. If, therefore, the meteoric period is nearly the same, the known
dates of star-showers indicate a diffusion of meteoroids around one half
of the orbit previous to the display of the year 15 B.C. No subsequent
perturbation, then, of a particular _part_ could sensibly effect the
general orbit of the stream. The infrequency of the display renders,
therefore, the hypothesis of a long period extremely improbable.
The entire interval between 687 B.C. and A.D. 1803 is 2490 years, or 92
periods of 27.0652 years; and the known dates are all satisfied by the
following scheme:
B.C. 687 to B.C. 15 .. 672 years = 25 periods of 26.8800 _y._ each.
15 to A.D. 582 .. 597 " = 22 " 27.1363 "
A.D. 582 to 1095 .. 513 " = 19 " 27.0000 "
1095 to 1122 .. 27 " = 1 " 27.0000 "
1122 to 1803 .. 681 " = 25 " 27.2400 "
With a period of 27 years, the perihelion being interior to the earth's
orbit, the aphelion distance of the meteors would be very nearly equal
to the distance of Uranus. The next shower, if the assumed period be
correct, ought to occur about 1884. It is worthy of remark that near the
time of the last (hypothetical) return Mr. Du Chaillu witnessed the
meteors of this epoch, in considerable numbers, in the interior of
Africa.
The Meteors of December 12.
Meteoric showers have occurred about the 12th of December in the
following years:
1. A.D. 901. "The whole hemisphere was filled with those meteors called
falling-stars from midnight till morning, to the great surprise of the
beholders in Egypt."
2. In 930 a remarkable shower of falling stars was observed in China.
3. Extraordinary meteoric phenomena were observed at Zurich at the same
epoch in 1571.
4. On the night of the 11th and 12th of December, 1833, a great number
of shooting-stars were seen at Parma. At the maximum as many as ten
were visible at the same time.
5. (Doubtful.) 1861, 1862, and 1863. Maximum probably in 1862. The
meteors at this return were far from being comparable in numbers with
the ancient displays. The shower, however, was distinctly observed.
R. P. Greg, Esq., of Manchester, England, says the period of December
12, 1862, was "exceedingly well defined."
These dates indicate a period of about 29-1/8 years. Thus:
901 to 930 1 period of 29.000 years.
930 to 1571 22 periods of 29.136 "
1571 to 1833 9 periods of 29.111 "
1833 to 1862 1 period of 29.000 "
Meteors of October 16-20.
Meteoric showers were observed from the 16th to the 20th of October in
the years 288, 1436, 1439, 1743, and 1798. These dates render it
somewhat probable that the period is about 27-1/2 years. Thus:
A.D. 288 to 1439 42 periods of 27.405 years each.
1439 to 1743 11 " 27.636 " "
1743 to 1798 2 " 27.500 " "
If these periods are correct, it is a remarkable coincidence that the
aphelion distances of the meteoric rings of April 20, October 18,
November 14, and December 12, as well as those of the comets 1866 I.,
and 1867 I., are all nearly equal to the mean distance of Uranus.
The Meteors of April 30, May 1.
Professor Schiaparelli, in his list of meteoric showers whose radiant
points are derived from observations made in Italy during the years
1868, 1869, and 1870, describes one as occurring on April 30 and May 1;
the radiant being in the Northern Crown. The same shower has also been
recognized by R. P. Greg, F.R.S., of Manchester, England. This
meteor-stream, it is now proposed to show, is probably derived from one
much more conspicuous in ancient times.
In Quetelet's "Physique du Globe" we find meteoric displays of the
following dates. In each case the corresponding day for 1870 is also
given,[28] in order to exhibit the close agreement of the epochs:
1. A.D. 401, April 9th; corresponding to April 29th, for 1870.
2. 538, " 6th; " April 25th, "
3. 839, " 17th; " May 1st, "
4. 927, " 17th; " April 30th, "
5. 934, " 18th; " May 1st, "
6. 1009, " 16th; " April 28th, "
[28] Making proper allowance for the precession of the equinoxes.
The epochs of 927 and 934 suggest as probable the short period of 7
years. It is found accordingly that the entire interval of 608
years--from 401 to 1009--is equal to 89 mean periods of 6.8315 years
each. With this approximate value the six dates are all represented as
follows:
From A.D. 401 to A.D. 538, 20 periods of 6.85 years.
538 to 839, 44 " 6.84 "
839 to 927, 13 " 6.77 "
927 to 934, 1 " 7.00 "
934 to 1009, 11 " 6.82 "
This period nearly corresponds to those of several comets whose aphelion
distances are somewhat greater than the mean distance of Jupiter. So
long as the cluster occupied but a small arc of the orbit the displays
would evidently be separated by considerable intervals. The comparative
paucity of meteors in modern times may be explained by the fact that the
ring has been subject to frequent perturbations by Jupiter.
Groups in which the Meteoroids are sparsely scattered.
By the labors of Heis, Greg, Herschel, Schiaparelli, and others, the
radiants of more than fifty sparsely strewn meteor-systems have been
determined. Of these the following, which are well defined, seem worthy
of special study:
DATE. POSITION OF RADIANT.
R. A. N. Decl.
January 1-4 234° 51°
January 18 232° 36°
April 25 142° 53°
The orbits and periods, except in the few cases previously considered,
are entirely unknown. Some of the observed clusters are probably the
_débris_ of ancient comets whose aphelia were in the vicinity of
Jupiter's orbit.